Determination and Speciation of Trace Elements in Foods
References .............................................................................................................. 192
Food is routinely analyzed for a variety of elements to assess possible nutritional or toxicological implications and to ensure compliance with government regulations or product quality1-3 and to determine authenticity or geographic origin.4 The level of a particular element varies greatly among the large variety of foods but is generally consistent for a particular food product. Element levels that may be considered safe or that ful‘ll a nutrient requirement may also be considered toxic at higher levels.5-8 Many elements routinely monitored in food have not been identi‘ed as nutrients or have not been found to be toxic at the levels normally found in food. The terms listed in Table 8.1 are used to conveniently describe the ranges of element mass fractions of interest in food. Element levels may be evaluated with respect to a speci‘c food or compiled for many foods and used to estimate dietary intakes. Duplicate diet or total diet studies are usually undertaken by national governments or large organizations to estimate intakes and assess the health of the population and safety of the food supply.9 Total-diet studies entail the analysis of a large number of foods selected on the basis of consumption. Duplicate-diet studies are another method for studying element intakes. In such studies, conducted over a relatively short period, a selected population provides a replicate portion size of the foods they consumed that is analyzed for the analytes of interest. These studies are usually designed to assess speci‘c exposure issues.10,11 Limited surveys of food are also performed and usually focus on a speci‘c food12,13 or category (e.g., infant food, dried desserts) collected at retail stores.14 The quality of the planning, collection, preparation, element analysis, and data evaluation determines the value of intake results from total-diet and duplicate-diet studies. Table 8.2 lists the elements most commonly monitored in foods, the usual purpose for their monitoring, and the usual range of interest. Many of these elements can be de‘ned as “metals,” but this term and the term “heavy metals” are discouraged since their meaning is not always understood.15 Many countries routinely monitor the level of elements in their foods,16-23 and compilations of element levels are available for some elements.24,25 The techniques commonly used for determining the levels of elements in foods are listed in Table 8.3
Horwitz26 has presented terminology for sampling and analytical operations that are useful for describing a “sample” through the various stages from collection to
TABLE 8.1 Terms for Mass Fraction Ranges
TABLE 8.2 Elements Commonly Monitored in Food
TABLE 8.3 Primary Determinative Techniques Used for Monitoring Elements in Food
analysis. The sample’s composition must not be adversely affected by contamination, change in moisture, or decay, for example, during the collection, shipping, storage, and preparation for analysis. Therefore, the containers used at each stage must be known not to contaminate the sample with the element(s) of interest or absorb the element from the sample. Hoenig27 has provided general guidance on preventing the problems during preparation of the analytical sample.